Atheism is the belief that nothing made everything. How can nothing make everything? What can nothing do? Nothing. You don't have to see God to believe in him. Who built the house? A builder? Who painted the painting? A painter? So the house and the painting didn't make themselves? All an atheist has to do is to look at creation and use some common sense. The atheist can also ask God to show him if he exists or not. God will answer him. Just ask him to prove whether he exists, and wait for an answer. Just say something like, "God, I don't know whether you exist or not. If you do exist, please let me know for sure."